1. Field of the Invention
The present invention relates to a display device such as rear-projection screen television, a transmission screen used for the display device, and a light diffusing substrate constituting the screen.
2. Description of Related Art
As one conventional transmission screen, there is known for example as shown in FIG. 2, a transmission screen which is generally used for a rear-projection screen television equipped with a CRT projector.
The screen normally includes in sequence from the viewer side, at least two lens sheet members, namely a dual-surface lenticular lens sheet 20 and a Fresnel lens sheet 10. In some cases, a flat protection sheet 30 is arranged at an outermost position on the viewer side.
The dual-surface lenticular lens sheet 20 is a lenticular lens sheet configured by forming on both sides, lens sections 22 and 23 of multiple oblong cylindrical lenses with the vertical direction as the longitudinal direction continuously arrayed in a horizontal direction. The lens section 22 on the projector side has a function for refracting and diffusing in the vertical direction image light projected from the projector, and the other lens section 23 on the viewer side has a function for modifying color shift (a problem of color shift of outgoing light attributable to a three-tube projector being arranged off-axis) by synergism with the lens section on the projector side.
On the other hand, for the image light to be seen by the viewer it is necessary to expand the viewing area not only in the horizontal direction but also in the vertical direction. In the vertical direction, the viewing area is expanded not by the refracting and diffusing function of the lens but by the diffusing function of a light diffusing material, and a method for applying the light diffusing material 24 to the lenticular lens sheet is employed.
In application of the light diffusing material, techniques have been appropriately employed such as, mixing the light diffusing material into the lenticular lens sheet itself to diffuse the light diffusing material into the interior of the lens sheet, or spread forming on the lenticular lens sheet, as a different member to the lens sheet, an ink containing the light diffusing material, or laminating on the lenticular lens sheet a resin sheet which has been extrusion formed with the light diffusing material mixed therein.
Furthermore, a typical configuration is where convex parts are provided at the boundaries of the cylindrical lenses on the viewing surface side of the dual-surface lenticular lens sheet, and a shading layer 25 is formed by printing or transfer forming a black ink onto the flat portion of the apexes thereof.
The main purpose for forming the shading layer 25 is to improve the contrast of the image seen, and to absorb external light so that reflection on the screen surface is not seen by the viewer.
In the dual-surface lenticular lens sheet 20, since there are irregularities on the exposed viewing surface side, dust and dirt are easily attached. Therefore, in some cases a protection sheet 30 is arranged for preventing the attachment of dust and dirt, and for protecting the shading layer.
Normally, on the surface of the protection sheet 31, it is general to provide a surface treatment layer 38 such as a hard coat for excoriation resistance, or an antistatic treated layer, or the like.
Recently, rather than the rear-projection screen television equipped with a CRT projector (hereunder called a CRT projection-type rear projection television), a rear-projection screen television equipped with a liquid crystal projector (hereunder called a liquid crystal projection-type rear projection television) having characteristics such as less power consumption, light weight, and thinness, has become popular.
Specifically, with upgrading of the image source such as to correspond to digital high definition, development of television of a format which uses the high definition liquid crystal panel is flourishing. Also in a liquid crystal projection-type rear projection television, a transmission screen that is bright with high resolution, that has a wide viewing angle in both the horizontal and vertical directions, that is superior in contrast, and that enables viewing of sharp images, has been sought.
In the case of the CRT projection-type rear projection television, as mentioned above, in order to correct for color shift caused by positional differences of the respective three tubes of RGB after image light is projected by means of the three tubes, the dual-surface lenticular lens sheet is used for the transmission screen. On the other hand, in the case of the liquid crystal projection-type rear projection television, the image light regulated by the liquid crystal panel is projected through a monocular lens, and so that color shift caused by positional differences does not occur, a single face lenticular lens sheet having a lens section on only one surface can be used for the transmission screen.
An example of the transmission screen used for the liquid crystal projection-type rear projection television is shown in FIG. 3.
The screen is configured by at least two members, namely a lenticular lens sheet 70 and a Fresnel lens sheet 60.
The lenticular lens sheet 70 is generally of a configuration where a lens section of multiple oblong cylindrical lenses with the vertical direction as the longitudinal direction continuously arrayed in a horizontal direction of the screen face, is formed on only one surface (single face lenticular lens sheet), and has a function for refracting and diffusing image light in the vertical direction.
On the flat surface on the opposite side to the lens section, which becomes the viewer side, a shading layer 75 is formed similarly to the case of the dual-surface lenticular lens sheet, to prevent reflection due to external light and improve the contrast of the image seen.
Furthermore, similarly to the case of the CRT projection-type rear projection television, it is necessary to widen the viewing area by the diffusing function of the light diffusing material, and a method for applying a light diffusing material to the lenticular lens sheet is employed.
The present applicant has proposed a lenticular lens sheet of a configuration where a light diffusing layer is formed on a shading layer of a single face lenticular lens sheet on Japanese Unexamined Patent Application, First Publication No. H09-120101.
As a light diffusing layer 80, techniques have been appropriately employed such as, spread forming ink containing the light diffusing material on the shading layer of the lenticular lens sheet, or laminating on the lenticular lens sheet a resin sheet (diffusing sheet) 84 which has been extrusion formed with the light diffusing material mixed therein.
In the latter, when the separately manufactured diffusing sheet 81 is adhered via an adhesion layer 87 to the lenticular lens sheet 70, it has the dual function of also imparting rigidity to the lenticular lens sheet.
The same figure gives a description related to the light diffusing layer 80 where a surface treatment layer 88 that effects a desired surface treatment (hard coat, antistatic, antireflection), is formed as necessary on the surface of the diffusing sheet 81.
In the light diffusing sheet 81 in which the light diffusing material is dispersingly mixed, the light diffusing material 84 is exposed from the surface, so the surface smoothness of the diffusing sheet is low.
Therefore, when the diffusing sheet 80 is laminated to the lenticular lens sheet 70, there are problems with handling such as, cohesiveness is not good, and selection of the adhesive 87 is limited.
As a patent application related to the light diffusing layer for the screen, Japanese Unexamined Patent Application, First Publication No. H11-271510 by the present applicant is well-known.
The above patent application is “a light diffusing sheet characterized in being formed by a three-layer configuration where front and back external layers are an optical transmittable resin, and an intermediate layer is an optical transmittable resin in which diffusive particles are dispersed.” The problems to be solved in this application are, a problem that in the case where an optical transmittable resin (intermediate layer) in which diffusive particles are dispersed, is laminated via an adhesive to another screen member (such as a lenticular lens sheet), the light diffusion characteristics change from the initial characteristics due to the influence of the adhesive; or a problem of adhesiveness between the light diffusing sheet and the other screen member when a surface condition is formed where the diffusive particles protrude from the intermediate layer. Since there is uncertainty about durability, and environmental changes such as temperature and humidity, the intermediate layer is protected and the smoothness of the surface is maintained by the optical transmittable resin of the front and back external layers.
Incidentally, there has been a demand for a light diffusing layer which is appropriate for screens in order to deal with problems peculiar to liquid crystal projection-type rear projection televisions.
In the liquid crystal projector, since the diameter of the projection pupil of the projection lens is small, then compared to the CRT projector, the following phenomena are noticeable.
A “hot bar” phenomenon where the brightness of the central point of incident light from the projector becomes a local high (hotspot), and bright stripes are observed in the direction of the parallel arrangement of the cylindrical lenses.
A “scintillation” phenomenon which is unnecessary flicker seen in the projected image.
In order to avoid hot bar, it is necessary to raise the light diffusion, and it is necessary to raise the light diffusion in a direction (vertical direction) perpendicular to the direction of the parallel arrangement of the cylindrical lenses.
Therefore, a proposal to enlarge the thickness of the light diffusing layer has been made by the present applicant as disclosed in Japanese Unexamined Patent Application, First Publication No. H10-83029.
On the other hand, in order to achieve high-definition of the image quality, it is desirable that the light diffusing layer be as thin as possible without causing a drop in resolution, resulting in a configuration in conflict with avoiding hot bar.
The present invention takes into consideration the above problems with the object of providing at a comparatively low cost a transmission screen, as a screen for a projection-type rear projection television (specifically, which uses a high-definition liquid crystal panel), that is bright with high resolution, that has a wide viewing angle in both the horizontal and vertical directions, that is superior in contrast, that enables viewing of sharp images, and further that reduces color shift.